1. Field of the Invention
The present invention relates to an optical disk device for performing recording and reproduction of digital data in/from an optical storage medium. More particularly, the present invention relates to techniques for recording and reproduction of digital data in/from a DVD-RAM (Digital Versatile Disk-Random Access Memory) or the like in which CAPA (Complementary Allocated Pit Addressing) exists, and for playback of an optical storage medium in which BCA (Burst Cutting Area) information exists.
2. Description of the Related Art
As a method for recording digital data on optical disk media as information storage media, there has commonly been employed a method of uniformizing the recording density on a storage medium by making the linear velocity constant, as seen in a compact disk (registered trademark; hereinafter referred to as a CD) and a digital versatile disk (hereinafter referred to as a DVD). In recent years, there have been employed as such storage media, not only a read-only optical disk, but also a writable DVD-Random Access Memory (hereinafter referred to as DVD-RAM), a write-once DVD-Recordable (hereinafter referred to as DVD-R), and a DVD-Rewritable (hereinafter referred to as DVD-RW). Among these media, the DVD-RAM disk is characterized by that it enables recording and reproduction of data by random access, and therefore, it is suitable as an information storage medium in a DVD recorder.
On a DVD-RAM disk, address information (Complementary Allocated Pit Addressing; hereinafter referred to as CAPA) has previously been recorded in an embossed area as shown in FIG. 21(a), and a capability of detecting the address information is one of factors that determine random access performance and recording/playback performance.
Hereinafter, a description will be given of an address detection unit included in a conventional DVD-PAM disk recording/playback apparatus.
FIG. 19 is a diagram illustrating an address detection unit for a conventional DVD-RAM disk, which is disclosed in Japanese Published Patent Application No. 2001-243714. This address detection unit performs address detection according to an analog signal processing method.
With reference to FIG. 19, an optical disk medium 1 is an optical storage medium having a thin film made of a phase change recording material, on which tracks are spirally or concentrically formed at regular intervals. A rewritable DVD-RAM disk as an example of the optical disk medium 1 has address information (CAPA) which is intermittently formed in an embossed area. A spindle motor 107 rotates the optical disk medium 1 at a predetermined linear velocity, and it is composed of a spindle motor, a stepping motor, and the like.
An optical pickup 3 writes and reads data into/from the optical disk medium 1. As shown in FIG. 2, the optical pickup 3 comprises an actuator on which a laser generation circuit 4 for focusing a light spot and scanning tracks is mounted, a four-split photodetector 5 for detecting a tracking error signal, which converts reflected light from the light spot into an electric signal, and a two-split photodetector 6 for detecting a focus error signal using two photodetectors 6a and 6b for short range and long range, respectively. The four-split photodetector 5 is divided into four regions 5a to 5d by a track direction axis and an axis perpendicular to the track direction axis.
As shown in FIG. 19, I/V converters 7 to 10 are current-to-voltage converters for converting detected currents outputted from the four photodetectors 5a to 5d into voltages, and I/V converters 77 and 78 are current-to-voltage converters for converting detected currents outputted from the two photodetectors 6a and 6b into voltages. An adder 11 adds the output voltages from the I/V converters 7 and 10, and an adder 12 adds the output voltages from the I/V converters 8 and 9. A balance adjuster 108 adjusts the balance between the output signals of the adders 11 and 12. A differential amplifier 109 generates a push-pull signal 14 on the basis of the output of the balance adjuster 108. A tracking error generator 110 generates a tracking error signal 17 from the push-pull signal 14. An equalizer 116 performs waveform equalization for the push-pull signal 14, and an address detector 117 detects address position information 41 and address polarity information 42 and 118 from the output signal of the equalizer 116. A wobble detector 115 detects a wobble signal that is caved along the tracks on the optical disk medium 1, binarizes the wobble signal, and outputs the binarized signal to an optical disk controller 16.
An adder 111 fully adds the output signals from the I/V converters 77 and 78 and the output signals from the adders 11 and 12 to generate a reproduction RF (Radio Frequency) signal 87. An AGC (Auto Gain Control) circuit 112 performs amplitude control for the reproduction RF signal 87, and an equalizer 81 equalizes the output waveform of the AGC circuit 112. An off-set cancel, unit 113 cancels oft-set components of the output signal from the equalizer 81, and a data slice circuit 114 binarizes the output signal from the off-set cancel unit 113. An optical disk controller 16 controls focus servo and tracking servo according to a tracking error signal 17 and a focus error signal.
Hereinafter, a description will be given of the operation of the address detection apparatus constituted as described above.
A laser beam emitted from the laser generation circuit 4 of the optical pickup 3 is reflected at the optical disk medium 1, and the reflected light beam is received by the divided regions 5a to 5d of the four-split photodetector 5. The four-split photodetector 5 outputs detection currents according to the amounts of light received by the respective divided regions, and the detection currents are converted into voltage values by the I/V converters 7 to 10. The output voltages from the I/V converters 7 and 10 are added by the adder 11 while the output voltages from the I/V converters 8 and 9 are added by the adder 12, and thereafter, these voltages are subjected to balance adjustment by the balance adjuster 108. The differential amplifier 109 detects a difference between the output of the adder 11 and the output of the adder 12, thereby generating a push-pull signal 14 as shown in FIG. 21(b) to be output to the tracking error generator 110, the equalizer 116, and the wobble detector 115.
High frequency components of the push-pull signal 14 outputted from the tracking error generator 110 are removed, whereby the push-pull signal 14 is converted into a tracking error signal 17. The wobble detector 115 detects a wobble signal that is carved along the tracks on the optical disk medium 1 and binarizes the signal, and outputs the binarized signal to the optical disk controller 16. The push-pull signal 14 outputted to the equalizer 116 is subjected to waveform equalization, and then inputted to the address detector 117, whereby address position information 41, address polarity information 42, and address polarity information 118 are detected. Hereinafter, the detail of the address detector 117 will be described with reference to FIGS. 20 and 21. FIG. 20 is a block diagram illustrating the construction of the address detector 117.
As shown in FIG. 20, the address detector 117 comprises comparators 119 and 120, an OR circuit 121, retriggerable monostable multi-vibrators 122 and 123, a charge pump 124, a capacitor 125, and a gate processing function 126.
The push-pull signal 14 shaped by the equalizer 116 is inputted to the comparators 119 and 120, and binarized with a predetermined threshold, and thereafter, inputted to the retriggerable monomulti vibrators 122 and 123 and to the OR circuit 121.
The outputs of the comparators 119 and 120 are logically added (hereinafter referred to simply as “added”) to each other by the OR circuit 121, and inputted as an address binarization pulse to the charge pump 124.
The charge pump 124 contains an analog switch and a current supply, and the address binarization pulse outputted from the OR circuit 121 is inputted to the charge pump 124. The charge pump 124 is constructed so that a charging current flows into the capacitor 125 during an “H” period of the address binarization pulse while a discharging current flows from the capacitor 125 during an “L” period of the address binarization pulse, when the CAPA area signal 25 is “H” and the analog switch is on. With this construction of the charge pump, charging and discharging of the capacitor 125 is carried out only during a period of header field (CAPA), whereby a threshold value 127 of the comparator 119 and a threshold value 128 of the comparator 120 are respectively fed back by the gate processing function 126 so that the pulse duty of the address binarization pulse that is gated by the CAPA area signal 25 is set to 50%, thereby generating an accurate binarization pulse.
Retriggerable monostable multi-vibrators (hereinafter referred to as retriggerable monomulti vibrators) 122 and 123 receive the output signals of the comparators 119 and 120, respectively, and output pulses during an appropriate period of time. Further, when the retriggerable monomulti vibrator receives a trigger input while it outputs the pulse, it outputs a pulse again from the point in time. The output signal of the retriggerable monomulti vibrator 122 is address polarity information 42 indicating an upper address as shown in FIG. 21(c), and the output signal of the retriggerable monomulti vibrator 123 is address polarity information 118 indicating a lower address as shown in FIG. 21(d). Address position information 41 showing a CAPA area is obtained as a signal shown in FIG. 21(e) by adding (OR addition) the address polarity information 42 and the address polarity information 118.
According to the above-mentioned operation, the address position information 41, the address polarity information 42, and the address polarity information 118 are detected by the address detector 117 on the basis of the output signals from the four-split photodetector 5.
On the other hand, the two detection currents outputted from the two-split photodetectors 6a and 6b are converted into voltage values by the I/V converters 77 and 78, respectively, and outputted to the adder 111. The adder 111 adds the output signals of the I/V converters 77 and 78 and the output signals of the adders 11 and 12, thereby generating a reproduction RF signal 87 in which all of the optical signals received by the four-split photodetector 5 and the two-split photodetector 6 are added.
The reproduction RF signal 87 is subjected to amplitude control by the AGC circuit 112, and thereafter, the waveform of the RF signal 87 is shaped so as to be easily binarized, and then the shaped signal is converted into a digital binarized signal 105 by the data slice circuit 114 via the offset cancel circuit 113. The digital binarized signal 105 is outputted to the optical disk controller 16.
The optical disk controller 16 drives the optical pickup 3 via a traverse drive circuit 130 and an actuator drive circuit 131 according to a tracking error signal 17 and a focus error signal, thereby performing focus servo and tracking servo. Further, the optical disk controller 16 performs demodulation of the recorded digital data using the digital binarized signal 105. At this time, the optical disk controller 16 generates a CAPA area signal 118 indicating a correct address area, performs tracking control so as to switch the track between a land track and a groove track alternately for every cycle, using the obtained address information, the address position information 41, the address polarity information 42, and the address polarity information 118, thereby alternately reproducing an address area and a digital data recorded area. Further, the optical disk controller 16 drives the spindle motor 107 via the spindle motor control circuit 132 on the basis of clock component information of the digital binarized signal 105.
In the conventional construction, however, when detecting the address position information and the address polarity information in the CAPA, since the front-side CAPA (hereinafter referred to as front CAPA) and the rear-side CAPA (hereinafter referred to as rear CAPA) which exist in the optical difference signal are separately detected, it is highly possible that continuity is lost in the vicinity of the middle of the address position information. This causes degradation in the address information detection accuracy, resulting in a reduction in the recording/reproduction performance of the optical disk device.
Further, in the above-mentioned conventional address detection apparatus, the analog filter for detecting the address position information and the address polarity information is required to change the filter multiplier for every recording/reproduction speed, resulting in increased circuit scale and increased power consumption.
Furthermore, when performing BCA (Burst Cutting Area) detection from an optical recording medium having a BCA in which information of the medium is described, the conventional construction cannot perform BCA detection.